sms.o4s.nl has no CNAME records.
Question and response
Question
dig sms.o4s.nl. NS
Answer
The response has no answer records.
Authority
o4s.nl. 3600 SOA nsauth1.pinkzuid.nl. hostmaster.pinkzuid.nl. 2024050103 28800 7200 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0